Late Cretaceous paleomagnetism of the Tombstone district and vicinity: Evidence for a rotational domain boundary in southeastern Arizona

Abstract

Paleomagnetic data are presented for Late Cretaceous volcanic and intrusive rocks in the Tombstone district and Dos Cabezas Mountains of southeastern Arizona. The resultant paleopole (73°N, 224°E, A95= 8°) is similar to a Late Cretaceous reference pole for North America (82°N, 210°E, A95= 7°), implying that these rocks have not been significantly rotated about vertical or near‐vertical axes relative to the continental interior. Generally, concordant results have also been published for Pennsylvanian terra rosa paleosols within the Black Prince Limestone at localities in the nearby Gunnison Hills, Whetstone Mountains, and Naco Hills. Together, however, these Carboniferous data indicate a 9°±7° clockwise rotation, with respect to North America, similar to that determined for the Colorado Plateau (5°–14°) since the mid‐Cretaceous. Published paleomagnetic data for rocks south and west of the Tombstone vicinity indicate much larger clockwise rotations ranging from ∼25° to ∼60°, implying that a rotational domain boundary runs between the Mustang Mountains and Canelo Hills to the southeast and between the Silver Bell and Tucson Mountains to the northwest. This boundary roughly coincides, in part, with the Sawmill Canyon fault zone and is parallel to other northwest trending strike‐slip faults in the region that were active during the Laramide orogeny. The clockwise rotations in southern Arizona are likely part of a larger pattern of dextral shear along the western margin of North America during the Late Cretaceous and early Tertiary caused by northward oblique subduction of oceanic plates relative to the stable craton.